Process for producing a fused fabric

ABSTRACT

In a process for producing a fused fabric a fluid is passed in contact with the surface of a fabric on the surface opposite that exposed to sufficient infrared radiation to fuse at least a portion of the synthetic thermoplastic fibers which comprise at least a portion of the fabric.

This is a continuation of application Ser. No. 905,072, filed May 11,1978 which is a division of Ser. No. 797,213 filed May 16, 1977, nowU.S. Pat. No. 4,105,484, issued Aug. 8, 1978.

BACKGROUND OF THE INVENTION

The present invention relates to a fused fabric and a method suitablefor producing a fused fabric.

It is frequently desirable to fuse together at least a portion of thefibers of a fabric. Such fabrics comprise at least a portion ofsynthetic thermoplastic fibers which melt and bond to adjacent fiberswhen the fibers are subjected to sufficient heat. The fabric may be awoven, knitted or nonwoven fabric; however, the fabric most often fusedis the nonwoven fabric. A variety of techniques are known in the art forfusing the fabrics noted above, such as by contacting such fabrics withheated rolls, hot fluids such as air, etc. More recently infraredradiation has been used to fuse various fabrics. While infraredradiation has proven to be a useful fusion technique, it is difficult tocontrol, particularly when the weight or thickness of fabric being fusedis not uniform. Thus, there is a need to improve infrared fusionprocesses in general. Further there is a need to improve infrared fusionprocesses for fusing nonuniform fabrics.

An object of the invention is the infrared fusion of fabrics.

Another object of the invention is the infrared fusion of fabrics inwhich control of the degree of fusion is substantially improved ascompared to the prior art.

According to the process of the invention a fabric, at least a portionof which comprises synthetic thermoplastic filaments, is contacted witha fluid on one surface and simultaneously the other surface is exposedto infrared radiation so that at least a portion of the syntheticthermoplastic fibers is fused together. This process produces a fusedfabric having an improved uniform appearance and a soft hand even inareas of the fabric in which the weight is relatively nonuniform.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to provide a better understanding of the invention a drawing isattached hereto in which:

FIG. 1 shows a perspective view partially cutaway of one embodiment ofan apparatus suitable for practicing the process of the invention, and

FIG. 2 shows a perspective view partially cutaway of another embodimentof an apparatus suitable for practicing the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Again referring to FIG. 1, an infrared heating means indicated generallyby reference numeral 10 comprises four infrared heaters 10a, 10b, 10cand 10d. Although only one infrared heater is necessary to practice theinvention, a group of heaters can be used as shown in the drawing. Ithas been found that the foil type electric heaters produce good results,although any type infrared heater can be employed including those usinggas or similar fuels instead of electricity.

The infrared heating means 10 is positioned adjacent to and spaced adistance from a conveying means 12 having an expanding width section 14and an essentially constant width section 16. A conveying means havingan expanding width section 14 and a constant width section 16 isfrequently referred to as a tenter frame and these are often used fortransporting nonwoven fabrics; however, most any conveying meanssuitable for transporting a fabric can be used whether it contains anexpanding width section or not provided the fabric is transported sothat the two surfaces of the fabric are unrestricted and exposedsimultaneously. The expanding width section of conveying means 12comprises rolls 23 and 24 and belts 26 and 28. Belts 26 and 28 have aplurality of pins 36 attached thereto extending outwardly so that theycan grasp the edges of fabric 40 passed to conveying means 12 via guiderolls 42, 43, and thus expose both surfaces of fabric 40 simultaneouslysince both surfaces are unrestricted. The constant width section 16 ofconveying means 12 comprises roll 24, which is also a part of theexpanding width section 14 described above, roll 30 and belts 32 and 34also having pins 36 attached thereto and extending outwardly. Fabric 40then passes under roll 44 to a suitable rollup device as known in theart. Roll 30 and/or roll 24 are usually driven by a suitable powersource (not shown).

In addition to infrared heating means 10 and conveying means 12, theapparatus also comprises a fluid-contacting means 17. In FIG. 1, thefluid-contacting means 17 comprises an elongated enclosure 18 having sixinlets 20 connected to a source of pressurized fluid such as compressedair and an outlet 22. In this embodiment outlet 22 comprises fourelongated openings or slots. It is desirable that each elongated openingbe fitted with vanes or a damper so that the direction and flow of thefluid can be regulated. Such vanes or dampers are well known in the artand are marketed commercially. For example, good results were obtainedemploying a commercial air diffusion device known as a Titus MODULinearmanufactured by the Titus Mfg. Corp., Waterloo, Iowa. Four Model ML-3400MODULinears were employed for the four elongated openings 22 shown inFIG. 1.

The apparatus shown in FIG. 2 is very similar to that shown in FIG. 1,the only difference being that the fluid-contacting means 50 of FIG. 2comprises a chamber having a perforated or porous flat surface such asscreen 52 and the fluid entering the chamber of fluid-contacting means50 via inlets 20 is dispersed and exits the chamber through theperforations in screen 52.

In the operation of the apparatus shown in FIG. 1, a fabric 40 is passedto conveying means 12 through guide rolls 42 and 43 and the edges of thefabric are grasped by the pins 36 in belts 26 and 28. As the distancebetween belts 26 and 28 becomes greater, fabric 40 is stretched in adirection normal to the direction of movement of the fabric. Fabric 40then passes over roll 24 and is grasped by pins 36 in belts 32 and 34.As fabric 40 passes beyond roll 30, it passes under roll 44 and then toa suitable roll-up device it is further processed as desired.

As fabric 40 passes between rolls 24 and 30, one side of fabric 40 isexposed to infrared radiation by infrared heating means 10 positionedadjacent to and spaced a distance from fabric 40 and the constant widthsection 16 of conveying means 12. Also as one side of fabric 40 is beingexposed to infrared radiation, the other side is simultaneouslycontacted with a fluid, such as air, as indicated by the arrows shown inFIG. 1. Although the temperature of the fluid can be selected over arelatively broad range, generally the temperature of the fluid is atambient temperature for most purposes of this invention and air is usedas the fluid.

In FIG. 2, the operation of the apparatus is essentially the same as forthe apparatus of FIG. 1. In FIG. 2 the fluid, such as air, entering thechamber of fluid contacting means 50 through a plurality of inlets 20connected to a suitable source of compressed air, not shown, exits thechamber through the perforations in screen 52 as indicated in thedrawing. Thus, the primary difference between the two embodiments of theinvention as shown in FIGS. 1 and 2 is that in FIG. 1 the air isdirected toward the surface of fabric 40 at an acute angle relative tothe surface of fabric 40 whereas in FIG. 2 the air is directedessentially perpendicular to the surface of fabric 40; but in eithercase an air pressure differential is created across the fabric whichcauses the air to pass through the fabric. In fabrics that are notuniform and have thick and thin spots, a larger volume of air movesthrough the thin spots which prevents the infrared radiation fromoverfusing these areas and that in turn produces a moreuniform-appearing fabric.

As shown in FIG. 1, the air contacting fabric 40 is directed upwardlyand generally in a countercurrent direction to the movement of fabric40, striking the fabric at an acute angle i.e., across the width of thefabric 40; however, fluid-contacting means 17 can be positioned nearroll 24 so that air can be directed concurrent to the direction of themovement of fabric 40 (not shown). Also it is possible to use twofluid-contacting means 17 as shown in FIG. 1 by positioning one suchmeans near roll 24 and one near roll 30 as shown in FIG. 1. Further, aplate can be used positioned adjacent fluid-contacting means 17 on theside of the fluid-contacting means 17 opposite fabric 40 and extendingparallel with the surface of fabric 40 contacted with fabric. The use ofsuch a plate restricts and contains the fluid near the surface of fabric40 which helps to induce a pressure differential across the fabric.

When using a tenter frame as the conveying means 12 as shown in FIGS. 1and 2, the fabric 40 is stretched in a direction normal or perpendicularto the direction of movement of the fabric and the fabric is stretchedimmediately prior to, during and immediately after fusing at least aportion of the synthetic thermoplastic fibers together.

Fabrics suitable for use in the invention include, for example, woven,knitted and nonwoven fabrics in which at least a portion of the fiberscomprising the fabric are synthetic thermoplastic fibers. It isenvisioned that the invention will find the greatest application fusingsynthetic thermoplastic nonwoven fabrics and it is with these fabricsthat the invention has been tested and found to produce very goodresults. Such nonwoven fabrics are well known in the art and areproduced by various well-known techniques such as for example air layingfibers or carding and crosslapping fibers to produce a batt followed byfusing, or the batt can be needled prior to fusing.

Most any synthetic thermoplastic filaments or fibers can be used infabrics fused according to the invention such as for examplepolyolefins, polyamides, polyesters and mixtures thereof. Apolypropylene nonwoven fabric was fused using the present invention withvery good results.

It is pointed out that the quantity and velocity of fluid required whichis contacted with the surface immmediately opposite the surface beingfused depend upon a number of variables and for that reason only generalguidelines are provided along with the specific example described below.The most important variables to be considered are the type andtemperature of contacting fluid, which for most applications will beambient air; the weight of the fabric to be fused and the relativenonuniformity, that is, the greater the nonuniformity the greaterquantity of contacting fluid required; the speed at which the fabric ismoving, the higher the speed the greater the quantity of contactingfluid required; the distance the infrared heating means is positionedfrom the surface of the fabric and the temperature of the infraredheating means; the type of synthetic thermoplastic fiber used in thefabric; and the angle of impingement of the fluid on the surface of thefabric, generally a lower flow rate of fluid is required when the fluidis directed normal to the surface of the fabric as compared to when thefluid is directed at an acute angle to the surface of the fabric.

EXAMPLE

In a specific example, a nonwoven web weighing about 3.1 oz/yd (73.47gm/sq meters) made of 31/4" (8.89 cm), 3 denier polypropylene staplefibers was fused in accordance with the invention. The fabric wassupported on a tenter frame about 5'6" (1.67 meters) wide in a manner asshown in FIG. 1. Four 4100 watt infrared heaters, Leeco Speed FoilHeaters manufactured by Joyal Industries, Inc., Coventry, R.I., wereoperated at 440 volts. The line speed was 30 FPM (9.14 m/m).

The plenum chamber for forcing air in contact with the surface of thefabric opposite the heaters was 10" (25.4 cm) wide, 10" high, and 5'0"(1.52 meters) long having four slots 1" (2.54 cm) wide and 5'0" (1.52meters) long positioned adjacent one another with the first slot 1"(2.54 cm) from the fabric similar to that shown in FIG. 1. The slotswere equipped with Titus Model ML-3400 MODULinears noted above. Thefirst two slots were adjusted to direct air toward the fabric with thetwo outer slots fully dampered. Air was provided to the bottom of thechamber by six 3" (7.62 cm) diameter inlets connected to a blower whichdelivered air at an average of 503 CFM (14.24 M³ /M) and at an averagevelocity of 940 FPM (286.5 m/m) from the slots. The fabric obtained hada substantially uniform appearance on both sides of the fabric and theside opposite the heaters had a uniform fuzzy texture and a soft hand.

Additional fabric was produced with the air supply turned off. Theappearance of this fabric indicated a noticeable loss in fabricuniformity apparently because there was a lack of fuzz in some areas onthe side opposite the heaters as compared to the fabric produced inaccordance with the invention described above. The fabric also possesseda harsh hand.

That which is claimed is:
 1. A process for the controlled fusing of atleast a portion of the synthetic thermoplastic fibers in an unfusedfabric, having a first and second surface, to produce a fused fabrichaving a uniform appearance and a soft hand, said process comprising thesteps of:exposing a portion of the first surface of said unfused fabricto infrared radiation to thereby fuse at least a portion of saidsynthetic thermoplastic fibers together; and directing a fluid towards aportion of the second surface of said unfused fabric, which is directlyopposite the portion of the first surface of said unfused fabric whichis exposed to said infrared radiation, in such a manner that at least aportion of said fluid passes completely through said unfused fabric soas to prevent overfusing of said synthetic thermoplastic fibers by saidinfrared radiation, the exposing of a portion of the first surface ofsaid unfused fabric to said infrared radiation occurring simultaneouslywith the directing of said fluid towards the portion of the secondsurface of said unfused fabric.
 2. A process in accordance with claim 1wherein said unfused fabric is a non-uniform fabric having varyingthicknesses and wherein the flow of said fluid is greater through thethinner areas of said unfused fabric than through the thicker areas ofsaid unfused fabric to substantially prevent said infrared radiationfrom overfusing the synthetic thermoplastic fibers in the thinner areasof said unfused fabric.
 3. A process in accordance with claim 1 whereinsaid unfused fabric is a nonwoven fabric.
 4. A process in accordancewith claim 1 wherein said synthetic thermoplastic fibers are selectedfrom the group consisting of polyolefins, polyamides, polyesters andmixtures thereof.
 5. A process in accordance with claim 1 wherein saidunfused fabric is a polypropylene nonwoven fabric.
 6. A process inaccordance with claim 1 wherein said fluid is air at ambienttemperature.
 7. A process in accordance with claim 6 wherein the air isdirected toward said first surface of said unfused fabric at an acuteangle relative to said first surface.
 8. A process in accordance withclaim 6 wherein the air is directed in an essentially perpendiculardirection relative to said first surface.
 9. A process in accordancewith claim 8 wherein said unfused fabric is stretched at least in afirst direction immediately prior to, during and immediately afterfusing said synthetic thermoplastic fibers.
 10. A process in accordancewith claim 9 wherein said unfused fabric is a polypropylene nonwovenfabric having been previously produced by crosslapping webs ofpolypropylene staple and needling the webs together.
 11. The fusedfabric produced according to the process of claim
 10. 12. The fusedfabric produced according to the process of claim 1.